linux-kernel - Re: [PATCH v12 08/54] ceph: add a has_stable

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Message-ID: <YkYJF07WdQZoucQ5@gmail.com>
Date:   Thu, 31 Mar 2022 20:03:35 +0000
From:   Eric Biggers <ebiggers@...nel.org>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     ceph-devel@...r.kernel.org, xiubli@...hat.com, idryomov@...il.com,
        lhenriques@...e.de, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 08/54] ceph: add a has_stable_inodes operation for
 ceph

On Thu, Mar 31, 2022 at 11:30:44AM -0400, Jeff Layton wrote:
>  static struct fscrypt_operations ceph_fscrypt_ops = {
>  	.key_prefix		= "ceph:",
>  	.get_context		= ceph_crypt_get_context,
>  	.set_context		= ceph_crypt_set_context,
>  	.empty_dir		= ceph_crypt_empty_dir,
> +	.has_stable_inodes	= ceph_crypt_has_stable_inodes,
>  };

What is the use case for implementing this?  Note the comment in the struct
definition:

       /*
         * Check whether the filesystem's inode numbers and UUID are stable,
         * meaning that they will never be changed even by offline operations
         * such as filesystem shrinking and therefore can be used in the
         * encryption without the possibility of files becoming unreadable.
         *
         * Filesystems only need to implement this function if they want to
         * support the FSCRYPT_POLICY_FLAG_IV_INO_LBLK_{32,64} flags.  These
         * flags are designed to work around the limitations of UFS and eMMC
         * inline crypto hardware, and they shouldn't be used in scenarios where
         * such hardware isn't being used.
         *
         * Leaving this NULL is equivalent to always returning false.
         */
        bool (*has_stable_inodes)(struct super_block *sb);

I think you should just leave this NULL for now.

- Eric